Efforts are continuing to pinpoint the precise stage at which streptomycin, spectinomycin, and erythromycin block initiating ribosomes, 2) to test the possibility that ribosomes read through successive genes on mRNA; and 3) to define the site of attachment of GTP on EF-Tu. We plan to initiate two new programs. One would test the hypothesis that excreted proteins are passed through the cell membrane while the nascent polypeptide is still attached to a ribosome. The other is based on the observation that certain antibiotics block free sensitive ribosomes but not polysomal ribosomes or free resistant ribosomes. This observation suggests that only the free sensitive ribosomes can expose the binding site, and this exposure may be revealed by the presence of a derivatizable SH or other group that is not accessible in the presence of the antibiotic or on the polysomal or the resistant ribosomes. BIBLIOGRAPHIC REFERENCES: Davis, B. D. Novel pressures on the advance of science. Ann. N.Y. Acad. Sci. 265-193-205 (1975). Davis, B. D. Discussion of "The social control of science." In A. Milunsky and G. J. Annas, Genetics and the Law, Plenum, 1976, 311-313.